Recording and reproducing head



E Mc/Vamee INVENTOR @ern ard B W EM ATTORNEY B. F. M NAMEE RECORDING ANDREPRODUCING HEAD Dec, 15, .1942.

Filed June 19 1959 Patented Dec. 15, 1942 l f RECORDDlG AND REPRODUCINGHEAD Bernard F. McNamee, Westwood. Calii'., assig'nor to UnitedAcoustigrapli Corporation, 7 Los Angeles, Calif., a corporation ofNevada Application June 19, 1939, serial No. 279.847

. V Claims. (CL 179100.41) This invention relates to a head that may'be' utilized in connection with recording and 'reproduction of. sound,vsuch for example, as for phonograph records, dictating machines, or thelike.

Heads of this character usually utilize a movable bar or armature ofmagnetic material, ar-

ranged between closely spaced opposing poles of a magnet. This armatureis usually mounted for oscillation about an axis transverse tothe-armature. The armature carries a stylus that is intended to. be incontact with the record or the record blank. Forrecording purposes, thearmature is influenced by an electromagnetic coil dis:- posedaround thearmature, and'which is fed with currents corresponding to the soundimpulsesto be recorded. The magnetic reaction between the armatureandthe magnet poles causes the stylus to oscillate in accordance with theimpulses to be recorded. The'oscillations are recorded on a film orblank by pressure or by cutting or engraving. 7

When the head is used for playback or reproduction, the stylus ismechanically moved in accordance with the record grooves; and suchmovements are caused to induce varying currents in theelectromagneticcoil. The current impulses may then be appropriatelyamplified and tively' much less force and it has been common to supportthestylus bars of such heads in rubber bushings. These are inexpensive,requireno adjustment and are free of: any looseness'or rattle. Whenheads. having stylus bars supported in this manner are usedforrecording, however, it has been found that the resilient bushing iscompressed allowing the axis of the stylusbar to move with theundesirable results just mentioned. It is accordingly a principal objectoi this invention to provide an improved type of support for the stylusbar in=such heads- It is another object of this invention to provide aheadthat is adapted to perform well for both recor'dingand reproduction.V v 1 g V It is another object .oithis invention to provide an improved.form of head of this general charutilized to operate "a translatingdevice such as a sound reproducer or secondary recorder.

It may seem that the head, appropriately designed for soundreproduction, would be immediately useful for recording. Actually,difierent requirements are imposed, so that {very often the recordingand playback functions are attained by the aid of separate devices. Y

Thus,in recording whether by embossing or cutting a record blank, thestylus is called upon to performanappreciable amount of work, and thestylus'bar which oscillates about an axis in the head accordingly iscalled upon to transmit force from the pole piece at its inner endto thestylus at its outer end. Under these conditions, f it is desirable toprevent any movement or looseness' of the stylus bar relative to itsaxialsupport, since such movement reduces the amplitude of movement ofthe stylus point as wel1 as introducing distortion. It'has been commonto profo'rm such axial support, but these require care- "ful adjustmentwhich is diflicult to maintain,

vide jewelled or other hard material pivots to;

w This invention possesses many other advan'- tages, and has otherobjects which may be madev more easily apparent from-a consideration ofone embodiment of the invention. For this purpose there is shown a formin the drawing accompanying and forming part of the presentspecification. Thisiorm will now be described in detail, illustratingthe general principles of the invention; but it is to be understood thatthis detailed description is not to be taken in a limiting sense, sincethe scope of this invention is best defined by the appended claims.Referring to the drawing: I g

Figure l is an enlarged sectional view of a head embodying theinvention;

Fig. 2 is a plan view, partlyin section, of the device shown in Fig. l;

Fig. 3 is a sectional view taken along plane I along plane 5-4 of Fig.4.

The reproduction and recording of impulses,

such'as sound impulses may be accomplished by the aid of thepresentapparatus. 'For this purpose use is made of a stylus 8. which isadapted to cooperate mechanically with a record or a record blank. Inorder to adapt this stylus both for reproduction as well as forrecordlngfltmay be appropriately formed with a suitable hard pointcapable of permanently deforming a record blank without cutting it, andcapable as well of following a record groove without injuryto th .endfaces 2 and 3, which are coplanar.

record. For this purpose the stylus 8 may be appropriately formed withsome gem point, such as a sapphire point.

In the present instance, asls quite common, .the stylus is arranged tobe supported on a magnetically influenced oscillatory armaturestructure, made from appropriate magnetic material. This armaturestructure includes a tubular socket member 9, having a lower saddleextension ID for guiding the insertion of the stylus 8 into the socket9. The socket 9 is shown as formed integral with a. flattened end memberor pole II, which is intended to cooperate with magnetic forces in amanner to be hereinafter described.

The armature structure is intended to be oscillatable about an axistransverse to the socket 9. For this purpose there are integrally formedoppositely directed extensions l2 and I3 which cooperate to form abearing structure for the armature structure 9| I. Furthermore, in orderto secure the stylus 8 in place, the upper extension I8 may be threadedfor the reception of a thumb clamping screw H.

The bearing support for the armature structure is shown to bestadvantage in Figs. 1, 2 and 5. 'Thus the extensions I2 and I3 arerespectively encompassed by the resilient 'sleeves l5 and I6. Thesesleeves may be of rubber or the like which resiliently resists any forcetending to move the'armature structureto an eccentric position withrespect to the sleeves [Sand I6.

The sleeves I5 and H; are adapted to be clamped between two clampingelements. One clamping element includes the inwardly turned ends' I! and|8 of a pair of supports, the structure of which will be hereinafterdetailed. The adjacent edges of the inwardly turned ends I! and I8 forma wedge shaped space contacting with the sleeves I5 and l6. They arefirmly held in the space by the aid of a clamping cap I9, which isapertured at its center for the free passage of the socket 8, outwardlyfrom the cap IS.

The inwardly turned ends I! and I8 are shown in this instance as formedintegrally with the side supporting plates 20 and 2|. These sup-.porting plates are arranged to provide a support for a magnet structure,such as the permanent horseshoe magnet This horseshoe magnetis shown asprovidedwith the downwardly directed These faces are placed in contactwith the right angle flanges 22 and 23 formed integrally with thesupports 20 and 2|, These flanges may furthermore be provided with theupturned edges 24 and 25 adapted to enga e the inner edges of the poleends of the magnet I.

The poles of magnet l are furthermore extended so as to provide anairgap 26 (Figs. 2 and 4) in which the flattened end' H of the armaturestructure is accommodated. This gap is formed by the aid of the inwardlybent polar extensions 4 andv 5, which may have their pole forming facesof reduced width, thereby restricting the areas of the poles. Thesepolar extensions 4 and 5 are integral with side members 6 and 1. Themembers 1 and 20, and 6 and 2| may be appropriately attached forexample, as by spot welding or the like. Thus the inwardly turned endsl1, l8 are in intimate magnetic contact with polar extensions 4' and 5respectively. i

' The polar extension members 6 and I are provided with flanges 21 and28 respectively. These flanges are intended to be disposed on top of anyappropriately formed bracket or support 28 extending across the bottomof the structure. In order to hold the magnet securely in place, a longscrew 30 may be provided, passing through the connecting portion of themagnet l and threaded into the support 29.

As thus far described, and as seen most clearly in Fig. 2, the armaturestructure is in the infiuence of the magnetism existing across the gap26 between the restricted opposed areas of the pole pieces 4 and 5.

During the operation of recording, the armature structure is variablypolarized by the aid of an electro-mag'net coil such as 3|, throughwhich a current passes corresponding to the impulses to be recorded. Thevarying magnetism of the armature causes its flattened polar end II tovibrate in the air gap 26. Thus, if the polar extension becomes thenorth pole, it will be attracted to the south pole of the air gap 26 andwill be repulsed from the north pole. It the armature structure, on theother hand, is so influenced as tocause the polar extension II to be asouth pole, the movement is in the reverse direction. For example, ifpole piece 4 and extension ll are north poles, and pole piece 5 andextension |8 are south poles, upon polar extension becoming anorth pole,it will be attracted toward pole piece 5, through the polar extensionII, to extension Conversely, upon the polar extension becoming a southpole, it will be, attracted toward pole piece 4, and the magnetic pathwill be from pole piece 4, through impressed by the stylus to form alaterally cut.

or indented record groove.

When the head is used for reproduction, the armature structure ismechanically vibrated or oscillated in the air gap by the contour of therecord groove with which the stylus 8 is in contact. This oscillationcauses the magnetic flux through the armature to vary as well as tochange polarity as the armature pole H is swung from it neutral positiontoward one or the other pole face. These variations in magnetism areutilized to induce an electromotive force in the coil 3| disposed aroundthe armature. This coil may thus serve for the dual purposeotinfiuencing the armature structure for recording purposes; and ofbeing influenced by the mechanical oscillation of the armature forreproducing purposes. y

In thepresent instance the coil 3| is diagrammatically illustrated asdisposed around the armature structure in the space formed between thepole pieces 4 and 5 and the inwardly turned extensions IT and |8.. Thusfor example it maybe supported on an insulation plate 32, as of fiber,fastened in any appropriate manner to the inner surfaces of the inwardlyturned ends I1 and I8. This supporting insulation member 32 isappropriately apertured for the accommodation of the armature. The coilleads 33 and 34 are shown as being connected to the metallic terminaleyelets 2,305,182 3 mension is in the direction of movement of the 35and 36 supported on the insulation plate 31. This insulation plate maybe appropriately fas- "tened to the top surface-of the bracket orsupport 29.

.7 If the armature pole extension ll is not per,- fectly centered in theair'gap 28, it will be attracted to'the nearer of the two poles, 4 and5, re- Theresulting in unsatisfactory" performance.

stylus, the bars are effective to prevent translatory movement of thearmature axis due tothe movement of thegstylus."

What is claimed is: v 1. In a head for recording and reproducing 1impulses, a magnet structure having symmetriiore, means must be providedto maintain the'pole extension ll centered in the" air gap 26'exceptwhen "force is applied'tothe armature; In recording, this force is dueto magnetic polarity induced in the armature pole extension I l by apul-'sating current in the coil 3|. In reproducing, this force is appliedmechanically by the undulations in the record groove acting to deflectstylus 8.

In both cases, it is desirable to have an armature bearing which permitsrotational movement of the armature structure about its axis, but whichdoes not permit translatory movement of the armature structure at itsaxis.

The amount of such translatory motion, that is,

a shifting of the armature axis in the direction advantages of lowcost'and freedom from looseness, means are provided to preventtranslatory motion of the armature structure, which means also functionsas a centering means. I

For this purpose resilient struts are arranged above and below thearmature structure and cooperate respectively with the extensions [2 and[3. These struts as shown most clearly in Figs. 1, 4, 5

and 6, may be in the form of the bar springs 38.

and 39.. Thesesprings are attached as by soldering or welding,respectively to the extensions l3 and I2 and extend transversely to theaxis of the extensions. They are anchored in clamps shown support 21 isprovided with inturned ears 40 and 4|, at its upper and lower edgesrespectively, each ear having a forwardly extending bar 42, 43. Clampingbars 44 and 45 are respectively slidably be readily placed in neutralposition when the armature structure is uninfiuenced. Thus, by adcallyspaced coplanar ends, supports respectively contacting the endsandextending transversely from the ends; said supports having opposed.inwardly turned projections, a .vlbratory armature structure supportedbythe aid of said projections to oscillate on an axis transverse. to theplane of the magnet ends, pole pieces for themagnet extending along thesupports and having opposed spaced poles with which the armaturecooperates, there being a space between the iriwardly turned projectionsand the spaced pole piece ends, and an electromagnetic coil surroundingthe armature and supported in'said space by the inwardly turnedprojections.

2. In a device of the character described, for

use in recording and reproducing impulses, an armature structure adaptedto carry a stylus and having means forming a pole, as well as transverseextensions adapted to form journals on opposite sides of the structure,a magnet having poles between which the pole of the armature structureis disposed, bearing structures cooperating respectively withsaidextensions to support the armature structure for oscillation about atransverse axis, each of said bearing structures including a sleeve ofresilient material -encircling I the extensions, and means whereby saidarmato best advantage in Figures 4, 5 and 6. Thus the r justing'each ofthe clamping bars 44 and 45 with I respect to the respective screw 41,adjustment of the armature structure about its axis is effected. In thisway the armature pole extension Il-may be readily centralized in the airgap 26.

The spring bars 38 and 39 are relatively easily deflected transversely,to permit suffieient movement of the armature about its axis. They aremade just stiff enough in this sense to ensure centering, At the sametime, these bars 38 and 39' have very great resistance to longitudinalcompression or extension, and thus prevent motion of the armature axisin the direction of the long dimension of the bars. Since this long di-'between themagnet poles, and whereby said armature structure axis isresiliently restrained from displacement in a directioncorresponding tothe axis of the armature when the armature is central betweensaid magnetpoles, said means comprising a pair of bar springs secured respectivelyto said extensions and extending in the direction of the desired strongrestraint.

. 3. In a stylus head for use in recording and reproducing impulses, an,armature structure adapted to carry, a stylus and having means forming apole as well as transverse extensions on opposite sides of thestructure, a magnet having poles between which the armature pole isdisposed, bearing structures cooperating respectively with saidextensions to resiliently support the armature structure for oscillationabout a transverse axis, and means'resiliently opposing said oscillationcomprising a pair of bar springs secured respectively tosaid extensionsand extending in the direction of the oscillatory movement whereby thesaid axis is prevented from moving in said direction.

4. In a stylus head for use'in recording and reproducing impulses, anarmature structure adapted to carry a stylus and having means forming apole as well as transverse extensions on opposite sides of thestructure, a magnet having poles between which the armature pole isdisposed, bearing structures cooperating respectively with saidextensions to resiliently support the armature structure 'foroscillation about a transverse axis, said extensions having ends projecting beyond said bearing structures, and a pair of bar springssecured respectively to said ends and extending transversely to saidextensions, said springs resiliently opposing said oscillation andpreventing translatory movement of the arq mature structure in thedirection of the oscillations.

5. In'a stylus headfor recording and repro- ,ducing impulses, anarmature structure adapted to carry a stylus and having means forming apole as well as transverse extensions adapted to form journals onopposite sides of the structure,

a magnet having poles between which the arma-:

ture pole is disposed, bearing structures cooperating respectively withsaid extensions to support.

the armature structure for oscillation about a transverse axis, each ofsaid bearing structures pole may be centered between the magnet poles.

BERNARD F. MCNAMEE.

